The present invention generally relates to capacitors for use with an Insulated Gate Bipolar Transistor (IGBT) and, more particularly, it relates to a capacitor module designed for direct mounting to an IGBT and a method for making the same.
An IGBT is a device that combines the features of a power transistor and a MOSFET. In particular, an IGBT has the high input impedance and high-speed characteristics of a MOSFET with the conductivity characteristics (low saturation voltage) of a bipolar transistor. See Dorf, The Electrical Engineering Handbook, CRC Press (1993), ISBN 0-8493-0185-8.
IGBTs are frequently used for power switching applications. In such applications, snubber circuits are used to "snub out" transient spikes generated by the IGBT when it switches from one state to another. It is known to use leaded capacitors in snubber circuits; however, the leads, which connect the capacitor(s) to the IGBT terminals, generate inductance and equivalent series resistance (ESR). Both of which lead to degraded performance of the snubber circuit and, consequently, degraded switching characteristics for the IGBT.
An additional drawback of using leads to connect capacitor(s) directly to IGBT terminals is uncertain reliability. Because leads are typically fragile and sensitive to vibration, they present a "weak link" in power applications which use IGBTs such as electric vehicles, motor applications, controllers, high power inverters and power conditioning systems.